Impact of high water carbon dioxide levels on Atlantic salmon smolts (<i>Salmo salar</i> L.): Effects on fish performance, vertebrae composition and structure

The role of high carbon dioxide (CO2) levels on fish performance, bone structure/composition and as a potential cause of spinal deformities was studied. Two groups of fish were exposed to a low (control) and a high level of CO, for 135 days during the freshwater period. After smoltification, the fish were transferred to seawater and followed up for 517 days until they reached harvest weight (3.1 kg BW). Differences in body weight between the control and high CO2 groups were observed. At the end of the freshwater period, average weight in the group exposed to high CO2 levels was 20.9% lower than in the control group. Specific growth rates (SGR) from the start of the experiment (10 g BW) to smolt stage were 1.63 +/- 0.04 and 1.36 +/- 0.01 for the control group and the high CO2 group, respectively. Differences in body weight were maintained during the initial stages of the seawater period, but were not observed at harvest weight. Nephrocalcinosis was not observed in any of the experimental groups at the end of the freshwater period and no external signs of spinal deformities were observed either at smolt stage or at harvest weight. X-rays revealed mild abnormalities in some vertebrae bodies, which could not be related to any experimental group. Despite the lack of signs of pathological bone alterations, the histological examination suggested that the exposure to high CO2 levels resulted in an increase in trabeculae volume and a higher rate of bone remodeling at the end of the freshwater period. Furthermore, fish exposed to a high CO2 level presented a higher bone ash content at the end of the freshwater period. These differences could not be observed at the end of the grow-out period

Intensification of landbased aquaculture production in single pass and reuse systems

Over the last 20 years, the productivity in hatcheries and farms producing fry and smolt of trout and salmon has increased substantially. These land-based farms are mainly situated along the coast and discharge effluent water directly to the sea. Such production is the basis of the recruitment of marine salmon and trout cage farms in Chile, Scotland, Norway and some other temperate countries with a coastline. Similarly, productivity and use of recirculation systems for the production of both seawater and freshwater fish has increased throughout the world. In many cases, the use of recirculation systems has ecological advantages over other technologies, especially those relying on flow through operations. The Norwegian authorities required a minimum flow supply of 1.5 m3 per 100,000 salmon smolt produced annually since the mid-80's. Without oxygenation of the water, the specific flow rate fluctuated between 0.5 and 2.5 L kg-1 min-1 throughout the year. Addition of pure oxygen then significantly reduced the flow requirements, now typically in the range 0.3 – 0.5 L kg-1 min-1. According to another regulation for licensing of hatcheries, the lowest allowable flow in single flow-through systems was 0.3 L kg-1 min-1. Water quality parameters have however been introduced recently as criterion instead of water flow requirements (concentrations of oxygen, carbon dioxide and ammonia). Mainly due to the usage of oxygenation technology, the water consumption at most smolt farms is at present 100 – 200 m3 kg-1 produced fish compared to 1,000 – 1,700 m3 kg-1 some 20 years ago. When the water flow is reduced, there is a build-up of both carbon dioxide and total ammonia, whilst pH is reduced. Both carbon dioxide and pH may become limiting factors when the water flow is decreased due to oxygen injection. There is however a lack of information regarding safe levels of carbon dioxide concentrations for Atlantic salmon smolts. Increased ventilation frequency and reduced growth have been observed in smolts exposed to reduced water flow. Effects observed during long-term experiments with rainbow trout and Atlantic salmon exposed to elevated carbon dioxide in fresh water include reduced growth and feed utilisation and nephrocalcinosis. Recirculation systems allow in the same time to reduce the make up water needs, to control the recirculated water quality and facilitates the treatment of the effluents (lower flow rate and higher concentration). They were developed at commercial scale in several countries and for various marine or freshwater fish species. In this article, some recirculation systems adapted to different fish life stages (from breeders to commercial size fish) and environments (Europe and USA) will be described. Improved feed quality, better feeding control and other factors have strongly reduced the waste production from farms. Since the mid-80's, the mean feed conversion ratio (FCR) in the Norwegian smolt industry as in other developed countries has decreased from 1.5 – 1.8 to less than 1.0 (kg feed kg-1 produced fish) which indicates a halved effluent load of organics and nutrients per kg produced fish. Additionally, many farms have introduced end-of-pipe treatment for solid removal before release to recipient

Cuttlebone calcification increases during exposure to elevated seawater PCo2 in the cephalopod Sepia officinalis.

Changes in seawater carbonate chemistry that accompany ongoing ocean acidification have been found to affect calcification processes in many marine invertebrates. In contrast to the response of most invertebrates, calcification rates increase in the cephalopod Sepia officinalis during long-term exposure to elevated seawater pCO2. The present trial investigated structural changes in the cuttlebones of S. officinalis calcified during 6 weeks of exposure to 615 Pa CO2. Cuttlebone mass increased sevenfold over the course of the growth trail, reaching a mean value of 0.71 ± 0.15 g. Depending on cuttlefish size (mantle lengths 44–56 mm), cuttlebones of CO2-incubated individuals accreted 22–55% more CaCO3 compared to controls at 64 Pa CO2. However, the height of the CO2-exposed cuttlebones was reduced. A decrease in spacing of the cuttlebone lamellae, from 384 ± 26 to 195 ± 38 μm, accounted for the height reduction The greater CaCO3 content of the CO2-incubated cuttlebones can be attributed to an increase in thickness of the lamellar and pillar walls. Particularly, pillar thickness increased from 2.6 ± 0.6 to 4.9 ± 2.2 μm. Interestingly, the incorporation of non-acid-soluble organic matrix (chitin) in the cuttlebones of CO2-exposed individuals was reduced by 30% on average. The apparent robustness of calcification processes in S. officinalis, and other powerful ion regulators such as decapod cructaceans, during exposure to elevated pCO2 is predicated to be closely connected to the increased extracellular [HCO3 −] maintained by these organisms to compensate extracellular pH. The potential negative impact of increased calcification in the cuttlebone of S. officinalis is discussed with regard to its function as a lightweight and highly porous buoyancy regulation device. Further studies working with lower seawater pCO2 values are necessary to evaluate if the observed phenomenon is of ecological relevance